Field of the Invention
The present invention relates generally to a small gas turbine engine and more specifically to a small turbine airfoil with impingement cooling and film cooling.
Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Since the invention of the gas turbine engine, much technological advancement have been introduced throughout the machine to increase the power, performance, and overall efficiency of the equipment. Many of these advancements have improved the efficiency of specific components, but the most significant improvements have been realized with the development of technologies that permit the temperature and pressure of the turbine working fluid to be increased. To this end, efficient turbine cooling represents an enabling technology that has put gas turbines in the forefront of a competitive means of producing power and propulsion in the modern marketplace.
Cooling of small turbine airfoils for small gas turbine engines pose additional challenges not seen in the larger engines. The primary challenges are manufacturing of the small features such as cooling holes and wall thicknesses needed for acceptable heat transfer performance. As cooling hole size decreases, discharge coefficient (Cd) decreases nonlinearly and thus require increased pressure drop which affects overall engine efficiency. In addition, acceptable film coverage becomes very difficult because the film holes approach a size where they cannot be shaped to provide adequate film protection.
A small gas turbine engine of the size used to power a UAV is typically formed with solid stator vanes that are cast as a single piece with the rotor disk. No cooling is used because the airfoils are too small for cooling passages. Stator vanes of this small size with cooling passages cannot be cast because the airfoil walls would be too thin.